The present invention relates to lubricant compositions and more particularly to biodegradable lubricants compositions especially useful as gear oils.
Commercially available lubricant compositions are prepared from a variety of natural and synthetic base stocks combined with various additive packages and solvents depending upon their intended application.
For lubricant applications requiring biodegradability of the lubricant base stock natural and synthetic ester base stocks have been extensively investigated. As might be expected no one ester will meet all of the major criteria specified for biodegradable lubricants. For example, one natural ester base stock in current use today is rapeseed oil which has very good biodegradability but poor low temperature properties and stability thus limiting its usefulness. An example of synthetic ester basestocks in current use are neopolyol esters formed by the esterification of neopolyols with mono- or dicarboxylic acids. For a given combination of neopolyol(s) and acid or acids there is a set of product properties that includes those such as viscosity, viscosity index, molecular weight, pour point, stability, demulsibility, and biodegradability, to mention just a few.
In those applications requiring biodegradable base stocks often it is also required that the lubricant additive employed with the base stock be substantially non-toxic. This is especially true if the lubricant composition is used on or near water or where it could possibly leak into the soil. Unfortunately many lubricant additives have poor environmental characteristics.
Experience has shown that most environmental type, gear oils are either biodegradable and non-toxic with poor performance in terms of gear protection and oil life, or they have good functional performance but lack the desired environmental characteristics. Thus, there is a need for a gear oil composition that has improved functional performances while maintaining low aquatic toxicity and biodegradability.
Accordingly, one object of the present invention is to provide improvements in gear performance of biodegradable non-toxic gear oils.
Another object of the present invention is to provide a gear oil composition that has balanced performance such as, for example, good rust inhibition without comprising FZG scuffing test performance.
These and other objects of the invention will become apparent from the description set forth below.
A biodegradable lubricating oil composition comprising:
(A) a major amount of a synthetic alcohol ester basestock formed by from the reaction product of:
(1) mono- and dipentaerythritol and (2) mixed acids comprising about 2 to 40 mole % linear mono carboxylic acids having from about 5 to about 12 carbon atoms, about 30 to about 70 wt % of a branched mono carboxylic acid having from about 15 to about 20 carbon atoms and from about 20 to about 30 mole % of a dicarboxylic acid or anhydride of a dicarboxylic acid having from about 4 to about 8 carbon atoms wherein the basestock has a viscosity at 100xc2x0 C. in the range of about 20 to about 50 cSt at 100xc2x0 C. and a pour point of less than about xe2x88x9220xc2x0 C.; and
(B) an effective amount of a polyoxyalkylene alcohol demulsifying agent, a combination of alkylated organic acid and ester thereof and ashless succinimide rust inhibitors and an ashless dithiocarbamate antiwear and extreme pressure agent.
The synthetic alcohol ester basestock used in the gear oils of the present invention is preferably formed from the reaction of mono- and dipentaerythritol and mixed acids. Typically the mole ratio of mono- to dipentaerythritol used is in the range of 80:20 to about 99.9:0.1.
The mixed acids employed in forming the esters comprises about 2 to 40 mole % linear mono carboxylic acids having from about 5 to about 12 carbon atoms, about 30 to about 70 wt % of a branched mono carboxylic acid having from about 10 to about 25 carbon atoms, preferably 15 to about 20 carbon atoms and from about 20 to about 30 mole % of a dicarboxylic acid having from about 4 to about 8 carbon atoms.
The synthetic esters are formed by reacting the mono- and dipentaerithritol with the mixed acids under conventional esterification conditions well known in the art. See for example, the Encyclopedia of Chemical Technology, Fourth Edition, Volume 9, pages 755-812 and the references cited therein.
The esters used in the compositions of the invention will have a viscosity in the range of about 20 to about 50 cSt at 100xc2x0 C. and a pour point of less than about xe2x88x9235xc2x0 C.
In an alternate embodiment a blend of esters formed as set forth above may also be used in formulation the gear oils of the invention.
Indeed in one embodiment two esters are used. One is the reaction product of (1) mono- and dipentaerythritol and (2) mixed acids comprising 30 to 40 mole % of C7 to C10 linear acids, from 24 to 28% of a dicarboxylic acid having 5 to 7 carbon atoms and from 34 to 40 mole % of a branched acid having 17 to 19 carbon atoms. The other is the reaction product of (1) above and (2) mixed acids comprising 2 to 6 mole % of C7 to C10 linear acids, form 25 to 29 mole % of a dicarboxylic acid and from 65 to 70 mole % of a branched acid having 17 to 19 carbon atoms.
The lubricant compositions of the invention are formed by blending the ester base stock together with at least an effective amount of a polyoxy-alkylene alcohol demulsifying agent, an ashless dithiocarbamate antiwear and extreme pressure agent, and a combination of alkylated organic acid and ester thereof and ashless succinimide rust inhibitors.
A suitable polyoxyalkylene alcohol demulsifying agent is characterized by the formula 
where EO is ethylene oxide moiety and PO is propylene oxide moiety, x and y represent the relative amounts of each. A preferred demulsifying agent will have a MW in the range of about 1700 to 3000 and an EO/PO ratio of from about 20/80 to about 1/99. Typically the polyoxyalkene alcohol demulsifying agent is dissolved in a solvent such as tricrylphosphate (TCP). Especially useful is a solution comprising from about 85 to 95 wt % TCP.
A suitable ashless dithiocarbamate antiwar and extreme pressure is characterized by the formula 
where R1 and R2 may be the same or different alkyl groups of from 1 to about 12 carbon atoms and preferably R1 and R2 are the same and have four carbon atoms.
Among suitable alkylated organic acids and esters thereof specific mention is made of alkylated succinic acid and esters thereof and especially tetra propenyl succinic acid and the monoester thereof where R is the monoester moiety, xe2x80x94COOR, is a C1 to C4 hydrocarbyl group. A mixture of about 70 wt % of the tetrapropenyl succinic acid and less than about 30 wt % of the ester is available as LZ 859 from Lubrizol Corporation, Wickliffe, Ohio.
Among suitable ashless succinimides known in the art specific mention is made of the reaction product of tetrapropenyl succinic anhydride and the intermediate product of oleic acid with triethyl amine. Such ashless succinimides are sold under the trade name Hitec 537 by Ethyl Corp., Richmond, Va. and under the trade name RT70B by ExxonMobil Chemical Company, Houston, Tex.
The composition of the invention may include other optional additives.
Preferably the additives listed in Table 1 are used in amounts sufficient to provide the normal function. Typical amounts for individual components are also set forth in the table. The balanced performance is achieved by carefully selecting the additives in the proper proportions to attain all of the necessary performance objectives.